Reheat boiler and gas temperature controlling method of reheat boiler

ABSTRACT

A reheat boiler according to the present invention includes a main boiler configured to make combustion gas originating from combustion in a burner flow from a furnace ( 102 ) and pass through a super heater and an evaporation tube bank, a reheat furnace ( 108 ) including a reheat burner ( 107 ) provided downstream of the evaporation tube bank, and a reheater ( 109 ) provided on the upper side of the reheat furnace ( 108 ), and also includes a combustion air supply portion ( 12 ) that is provided at a position opposite to the reheat burner ( 107 ) in the reheat furnace ( 108 ) to supply a part of the combustion air as combustion air ( 11   b ). By making combustion gas ( 107   a ) and the combustion air ( 11   b ) collide head-on to facilitate mixing of the combustion gas ( 107   a ) with the combustion air ( 11   b ), the flow patterns of the combustion gas are changed, whereby temperature unevenness of the combustion gas ( 107   a ) at the outlet of the reheat furnace ( 108 ) is reduced.

TECHNICAL FIELD

The present invention relates to a reheat boiler including a reheatfurnace and a reheater provided downstream of an evaporation tube bankand reducing temperature unevenness of combustion gas near an outlet ofthe reheat furnace and to a gas temperature controlling method of such areheat boiler.

BACKGROUND ART

Marine boilers including a super heater have been widely used (PatentDocument 1). Furthermore, reheat boilers including a reheat furnace anda reheater provided downstream of combustion gas in conventional marineboilers have been used.

An exemplary configuration of the conventional marine reheat boiler isillustrated in FIG. 6. FIG. 6 is a schematic of a configuration of theconventional reheat boiler. As illustrated in FIG. 6, this conventionalreheat boiler 100 includes: a main boiler 106 including a burner 101, afurnace 102, a front tube bank 103, a super heater (SH) 104, and anevaporation tube bank (rear tube bank) 105; a reheat furnace 108including a reheat burner 107 provided downstream of the evaporationtube bank 105; and a reheater 109 provided at a combustion gas outletside. The combustion gas originating from combustion in the burner 101flows from the furnace 102, passes through the front tube bank 103, theSH 104, and the evaporation tube bank 105, and is mixed with thecombustion gas originating from combustion in the reheat burner 107 inthe reheat furnace 108. With its heat exchanged with the reheater 109,the gas further flows, and is output from a gas outlet 110. The reheatboiler is thus operated efficiently.

In FIG. 6, the numeral 111 indicates a water drum, the numeral 112indicates a steam drum, the numerals 113, 114 indicate headers, and thenumeral 115 indicates a wall tube.

[Patent Document 1] Japanese Patent Application Laid-open No.2002-243106.

DISCLOSURE OF INVENTION Problem to be Solved by the Invention

The conventional marine reheat boiler 100 includes the reheat burner 107on a front wall side of the reheat furnace 108, but not on a rear wallside of the reheat furnace 108. Because of this configuration, asillustrated in FIG. 7, large temperature unevenness of the combustiongas arises between the front wall side (indicated by the letter X inFIG. 7) and the rear wall side (indicated by the letter Y in FIG. 7) ofthe reheat furnace 108 on the outlet side thereof (indicated by theletter B in FIG. 6).

Temperature unevenness of the combustion gas on the outlet side of thereheat furnace 108 (that is, on the inlet side of the reheater 109)deteriorates heat conductivity of the reheat furnace 108 and thereheater 109, and may also cause high-temperature corrosion of reheatertubes and strength drops of support members in the reheater 109. Theletter A in FIG. 7 indicates where the reheat burner is provided, andthe letter C indicates the outlet portion of the reheater 109.

In view of the above problems, an object of the present invention is toprovide a reheat boiler and a gas temperature controlling method of areheat boiler that change gas flow patterns of a reheat burner to reducetemperature unevenness of combustion gas on the outlet side of a reheatfurnace.

Means for Solving Problem

According to an aspect of the present invention, a reheat boiler thatincludes a main boiler in which combustion gas produced by combustion ina burner flows through a super heater and an evaporation tube bank froma furnace, a reheat furnace with a reheat burner provided downstream ofthe evaporation tube bank, and a reheater provided on an upper side ofthe reheat furnace, includes a combustion air supply portion that isprovided at a position opposite to the reheat burner in the reheatfurnace to supply a part of combustion air.

Advantageously, in the reheat boiler, at least two stages of suchcombustion air supply portions are provided in a height direction of thereheat furnace.

Advantageously, in the reheat boiler, a part of the combustion air issupplied to the combustion air supply portion by a rate of 50% or less.

Advantageously, in the reheat boiler, at least two stages of suchcombustion air supply portions are provided in a height direction of thereheat furnace, and each stage of the combustion air supply portionssupplies a different volume of the combustion air.

According to another aspect of the present invention, a gas temperaturecontrolling method of the above mentioned reheat boiler includes:supplying a part of the combustion air into the reheat furnace from aposition opposite to the reheat burner to reduce temperature unevennessof the combustion gas on an outlet side of the reheat furnace.

Effect of the Invention

According to the present invention, by providing the combustion airsupply portion at a position opposite to the reheat burner in the reheatfurnace to supply a part of the combustion air to the reheat furnace,flow patterns of gas discharged from the reheat burner can be changed.Therefore, temperature unevenness of the combustion gas on the outletside of the reheat furnace is reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1A is a schematic of the configuration of a reheat furnace and areheater included in a reheat boiler according to a first embodiment ofthe present invention.

FIG. 1B is a sectional view seen in a direction perpendicular to thevertical direction of the reheat furnace illustrated in FIG. 1A.

FIG. 2 is a schematic of the configuration of the reheat boileraccording to the first embodiment of the present invention.

FIG. 3 is an illustrative view of the temperature distribution ofcombustion gas at the outlet of the reheat furnace.

FIG. 4 is a schematic of the configuration of a reheat boiler accordingto a second embodiment of the present invention, extracting its reheatfurnace and reheater alone.

FIG. 5 is an illustrative view of the temperature distribution ofcombustion gas near the outlet of the reheat furnace.

FIG. 6 is a schematic of an exemplary configuration of a conventionalreheat boiler.

FIG. 7 is an illustrative view of the temperature distribution near theoutlet of a conventional reheat furnace.

EXPLANATIONS OF LETTERS OR NUMERALS

10A, 10B reheat boiler

-   11, 11 b-1 to 11 b-3 combustion air-   12, 12-1 to 12-3 combustion air supply portion-   101 burner-   102 furnace-   103 front tube bank-   104 super heater (SH)-   105 evaporation tube bank (rear tube bank)-   106 main boiler-   107 reheat burner-   108 reheat furnace-   109 reheater-   110 gas outlet-   111 water drum-   112 steam drum-   113, 114 header-   115 wall tube

BEST MODE(S) FOR CARRYING OUT THE INVENTION

The present invention will be described in detail with reference to theaccompanying drawings. The embodiments below are not intended to limitthe scope of the present invention. Elements described in theembodiments include their variations readily thought of by those skilledin the art and substantially equivalent elements.

First Embodiment

A reheat boiler according to an embodiment of the present invention willnow be described with reference to some drawings.

The reheat boiler according to the present embodiment has a similarconfiguration to that of a conventional reheat boiler as illustrated inFIG. 6 and has an air supply portion provided to a reheat furnace;therefore, like elements have like reference numerals, and repeateddescriptions will be omitted.

FIG. 1A is a schematic of the configuration of the reheat furnace and areheater included in the reheat boiler according to the first embodimentof the present invention, and is a sectional view along the line I-I inFIG. 2. FIG. 1B is a sectional view seen in a direction perpendicular tothe vertical direction of the reheat furnace illustrated in FIG. 1A.FIG. 2 is a schematic of the configuration of the reheat boileraccording to the first embodiment of the present invention.

In FIGS. 1A and 1B, the letter X represents a front wall side of thereheat furnace, and the letter Y represents a rear wall side of thereheat furnace.

Referring to FIGS. 1A, 1B, and 2, this reheat boiler 10A according tothe present embodiment includes, like the configurations of conventionalreheat boilers as illustrated in FIG. 6, the main boiler 106 configuredto make combustion gas originating from combustion in the burner 101flow from the furnace 102 and pass through the SH 104 and theevaporation tube bank 105, the reheat furnace 108 in which thecombustion gas is reburned with the reheat burner 107, and the reheater109 through which the reburned combustion gas passes. Referring to FIGS.1A and 1B, the reheat boiler 10A also includes a combustion air supplyportion 12 provided at a position opposite to the reheat burner 107 inthe reheat furnace 108 to supply a part of combustion air 11 a to besupplied to the reheat burner 107 as combustion air 11 b.

According to the present invention, the combustion air 11 a refers tocombustion air that is a part of the combustion air 11 and is suppliedto the reheat burner 107, while the combustion air 11 b refers tocombustion air that is another part of the combustion air 11 remainingafter being allocated to the reheat burner 107 and is supplied to thecombustion air supply portion 12.

By providing the combustion air supply portion 12 at the positionopposite to the reheat burner 107 in the reheat furnace 108, combustiongas 107 a discharged from the reheat burner 107 and the combustion air11 b supplied through the combustion air supply portion 12 collidehead-on with each other, which facilitates mixing of the combustion gas107 a with the combustion air 11 b. Consequently, temperature unevennessof the combustion gas 107 a at the outlet of the reheat furnace 108 canbe reduced.

FIG. 3 is an illustrative view of the temperature distribution of thecombustion gas at the outlet of the reheat furnace illustrated in FIG.1A. As indicated in FIG. 3, by providing the combustion air supplyportion 12 at the position opposite to the reheat burner 107 in thereheat furnace 108 and supplying the combustion air 11 b into the reheatfurnace 108, the temperature distribution of the combustion gas 107 anear the outlet of the reheat furnace 108 (indicated by the letter B inFIGS. 1A and 2) falls within a range from 600 to 800 degrees Celsius,for example. With the average temperature being kept about 700 degreesCelsius, this range is narrower than the temperature distribution of thecombustion gas 107 a near the outlet of the reheat furnace 108(indicated by the letter B in FIGS. 6 and 7) included in theconventional reheat boiler 100 as indicated in FIG. 7.

By thus supplying the combustion air 11 into the reheat furnace 108 fromthe position opposite to the reheat burner 107, temperature unevennessnear the outlet of the reheat furnace 108 can be suppressed comparedwith the temperature of the combustion gas 107 a near the outlet of thereheat furnace 108 (indicated by the letter B in FIGS. 6 and 7) includedin the conventional reheat boiler as indicated in FIG. 7.

In the reheat boiler 10A according to the present embodiment, thecombustion air 11 b that remains after subtracting the combustion air 11a to be supplied to the reheat burner 107 from the combustion air 11 issupplied through the combustion air supply portion 12 preferably by arate of 50% or less. This is because allocating a majority of thecombustion air 11 to the combustion air 11 b will cause incompletecombustion of fuel in the reheat burner 107.

In the reheat boiler 10A according to the present embodiment, thecombustion gas 107 a is first burned with the combustion air 11 asupplied into the reheat burner 107 and then with the combustion air 11b supplied through the combustion air supply portion 12 in astep-by-step manner. Burning the combustion gas 107 a in two stages withthe combustion air 11 a and the combustion air 11 b can suppress theformation of NO_(x).

In the reheat boiler 10A according to the present embodiment, the airvolume of the combustion air 11 b supplied through the combustion airsupply portion 12 is adjusted with, for example, a damper or other airvolume adjusters.

In the reheat boiler 10A according to the present embodiment, bysupplying the combustion air 11 b into the reheat furnace 108 throughthe combustion air supply portion 12 provided at the position oppositeto the reheat burner 107 in the reheat furnace 108, the flow patterns ofthe combustion gas 107 a discharged from the reheat burner 107 can bechanged. Accordingly, temperature unevenness of the combustion gas 107 aon the outlet side of the reheat furnace 108 can be reduced. Thisconfiguration prevents heat conductivity drops of the reheat furnace 108and the reheater 109 and also prevents high-temperature corrosion ofreheater tubes and strength drops of support members in the reheater109.

Second Embodiment

A reheat boiler according to a second embodiment of the presentinvention will now be described with reference to FIGS. 4 and 5.

FIG. 4 is a schematic of the configuration of the reheat boileraccording to the second embodiment of the present invention, extractingits reheat furnace and reheater alone.

The reheat boiler according to the present embodiment has a similarconfiguration to that of the reheat boiler according to the firstembodiment; therefore, like elements have like reference numerals, andrepeated descriptions will be omitted.

Referring to FIG. 4, this reheat boiler 10B according to the presentembodiment includes three-staged combustion air supply portions 12-1 to12-3 disposed at intervals in the height direction of the reheat furnace108 and at positions opposite to the reheat burner 107 in the reheatfurnace 108.

By supplying the combustion air 11 b-1 to 11 b-3 into the reheat furnace108 through the air supply portions 12-1 to 12-3, the mixture degrees ofcombustion gas with the combustion air 11 b-1 to 11 b-3 can be adjusteddesirably, whereby the temperature distribution of the combustion gasnear the outlet of the reheat furnace 108 can be controlled.

In the boiler 10B according to the present embodiment, the flow rates ofthe combustion air 11 b-1 to 11 b-3 supplied through the air supplyportions 12-1 to 12-3, respectively, are adjustable thereby. Byadjusting the flow rates of the combustion air 11 b-1 to 11 b-3 suppliedinto the reheat furnace 108, the mixture degrees of the combustion gas107 a with the combustion air 11 b-1 to 11 b-3 can be adjusted, wherebythe temperature distribution near the outlet of the reheat furnace 108can be controlled. For example, by making the air volume of thecombustion air 11 b-1 relatively large and the air volumes of thecombustion air 11 b-2 and the combustion air 11 b-3 even, thetemperature distribution near the outlet of the reheat furnace 108 canbe smoothed.

FIG. 5 is an illustrative view of the temperature distribution of thecombustion gas near the outlet of the reheat furnace illustrated in FIG.4. By adjusting the flow rates of the combustion air 11 b-1 to 11 b-3supplied through the combustion air supply portions 12-1 to 12-3 asillustrated in FIG. 4, temperature unevenness of the combustion gas 107a on the outlet side of the reheat furnace 108 can be reduced asindicated in FIG. 5.

By thus supplying the combustion air 11 b into the reheat furnace 108 inmultiple stages, the temperature distribution of the combustion gas 107a near the outlet of the reheat furnace 108 (indicated by the letter Bin FIG. 4) falls within a range from 620 to 780 degrees Celsius, forexample. With the average temperature being kept about 700 degreesCelsius, this range is narrower than the temperature distribution of thecombustion gas 107 a near the outlet of the reheat furnace 108(indicated by the letter B in FIG. 6) included in the conventionalreheat boiler 100 as indicated in FIG. 7.

This configuration can achieve a smoother temperature distribution thanthe temperature distribution of the combustion gas 107 a near the outletof the reheat furnace 108 (indicated by the letter B in FIG. 2) includedin the reheat boiler 10A according to the first embodiment as indicatedin FIG. 3.

By thus supplying the combustion air 11 b-1 to 11 b-3 into the reheatfurnace 108 from the positions opposite to the reheat burner 107 andfinely adjusting the air volumes of the combustion air 11 b-2 and thecombustion air 11 b-3, temperature unevenness near the outlet of thereheat furnace 108 can be suppressed.

Fine adjustment of the flow rates of the combustion air 11 b-1 to 11 b-3can in turn adjust temperature, retention time, and other conditions ofan area where reduction takes place, thereby suppressing the formationof NO_(x). For example, making the flow rate of the combustion air 11b-1 small and the flow rate of the combustion air 11 b-3 large to causea shortage of air in the reheat furnace 108 can suppress the formationof NO_(x).

Accordingly, in the reheat boiler 10B according to the presentembodiment, by delivering the combustion air 11 b-1 to 11 b-3 throughthe combustion air supply portions 12-1 to 12-3 disposed at intervals inthe height direction and at the positions opposite to the reheat burner107 in the reheat furnace 108 and finely adjusting the flow rates of thecombustion air 11 b-1 to 11 b-3 supplied into the reheat furnace 108,the gas flow patterns from the reheat burner 107 can be changed.Consequently, temperature unevenness of the combustion gas 107 a on theoutlet side of the reheat furnace 108 can be further reduced. Thisconfiguration prevents heat conductivity drops of the reheat furnace 108and the reheater 109 and also prevents high-temperature corrosion of thereheater tubes and strength drops of the support members in the reheater109.

The mixture degrees of the combustion gas 107 a with the combustion air11 b-1 to 11 b-3 can be finely adjusted, whereby the temperaturedistribution at the outlet of the reheat furnace 108 can be controlled.Furthermore, fine adjustment of the air volumes of the combustion air 11b-1 to 11 b-3 can in turn adjust conditions of an area where reductiontakes place in the reheat furnace 108, thereby suppressing the formationof NO_(x).

While three stages of the combustion air supply portions 12-1 to 12-3are disposed at intervals in the height direction of the reheat furnace108 in the reheat boiler 10B according to the present embodiment, thepresent invention is not limited thereto. Three or more stages of suchair supply portions 12 may be provided.

With the reheat boilers 10A and 10B according to the present invention,by supplying a part 11 b of the combustion air into the reheat furnace108 from the position(s) opposite to the reheat burner 107 in the reheatfurnace 108, the flow patterns of the combustion gas are changed,whereby temperature unevenness of the combustion gas on the outlet sideof the reheat furnace 108 can be reduced. Therefore, they are applicablefor marine boilers; however, the present invention is not limitedthereto.

INDUSTRIAL APPLICABILITY

As described above, the reheat boilers and methods for adjusting thetemperature of gas output from a reheat boiler according to the presentinvention can change the flow patterns of combustion gas by supplying apart of combustion air into a reheat furnace through at least onecombustion air supply portion disposed at intervals in the heightdirection of the reheat furnace and at position(s) opposite to a reheatburner in the reheat furnace. Therefore, they are applicable for marinereheat boilers intended to reduce temperature unevenness of thecombustion gas on the outlet side of the reheat furnace.

1. A reheat boiler that includes a main boiler in which combustion gasproduced by combustion in a burner flows through a super heater and anevaporation tube bank from a furnace, a reheat furnace with a reheatburner provided downstream of the evaporation tube bank, and a reheaterprovided on an upper side of the reheat furnace, the reheat boilercomprising: a combustion air supply portion that is provided at aposition opposite to the reheat burner in the reheat furnace to supply apart of combustion air.
 2. The reheat boiler according to claim 1,wherein at least two stages of such combustion air supply portions areprovided in a height direction of the reheat furnace.
 3. The reheatboiler according to claim 1, wherein a part of the combustion air issupplied to the combustion air supply portion by a rate of 50% or less.4. The reheat boiler according to claim 1, wherein at least two stagesof such combustion air supply portions are provided in a heightdirection of the reheat furnace, and each stage of the combustion airsupply portions supplies a different volume of the combustion air.
 5. Agas temperature controlling method of the reheat boiler according toclaim 1, the method comprising: supplying a part of the combustion airinto the reheat furnace from a position opposite to the reheat burner toreduce temperature unevenness of the combustion gas on an outlet side ofthe reheat furnace.